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<head>
  <meta charset="UTF-8">
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  <title>Document</title>
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<body>
  <script>
    var isValid = function (s) {
      let n = s.length / 2
      while (s.length != n) {
        n = s.length
        s = s.split('abc').join('')
      }
      if (s == '') return true
      return false
    };
    console.log(isValid("abccba"))
  </script>
</body>

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